The major emphasis of this research program will focus on the ocular physiology of the teleost. Preliminary results indicate that carbonic anhydrase is an essential component of the counter current oxygen multiplier found in the teleost choroid, consisting of a rete mirabile. The anatomical description of these vessels and the histochemical localization of carbonic anhydrase within them will be determined and correlated with our hypothesis of counter current oxygen multiplication. The influence of hyperbaric tensions on teleosts and other vertebrate retinas will be investigated. Initial studies indicate that the teleost retina is resistant to oxygen toxicity, whereas frog retinas are not. Utilizing intracellular recording techniques and analysis of transmembrane resting potentials the susceptibility of various cell types in the retina will be investigated. In addition, the influence of hyperbaric oxygen on Na ion minus K ion ATPase will be examined. We propose that the resistance to oxygen toxicity is mediated through an isozyme of superoxide dismutase. Separation and qualitative identification of the enzyme will be done, initially by electrophoretic separation. Further kinetic data on selected isozymes will be determined through the use of a modified superoxide dismutase assay using a hanging drop mercury polarographic electrode.